phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('27812f78d1f36715dd44fa5c44f10db7', -1, 1432864640, 1432864640, '3691a660', -1, 0, 0)

Line : 187
File : sessions.php